This invention relates to a method of detecting a drastic change between two adjacent ones of successive pictures represented by an input digital video signal. This invention relates also to a detecting device for use in carrying out the method.
The input digital video signal is, for example, a television signal. Each of the successive pictures comprises a predetermined number of picture elements and corresponds to a frame of the input digital video signal.
As will later be described, a conventional detecting method makes use of a correlation between two successive pictures in order to detect the drastic or large change, such as a scene change, between two adjacent ones of successive pictures. More specifically, a frame memory delays the input digital video signal into a delayed digital video signal having a delay which is equal to one frame of the input digital video signal. A subtracter produces a difference signal representative of a difference between the input digital video signal and the delayed digital video signal. Responsive to the difference signal, a first comparator compares an absolute value of the difference with a first threshold value for each picture element to produce first and second comparison result signals when the absolute value is greater than the first threshold value and when the absolute value is not greater than the first threshold value, respectively. A counter counts the first comparison result signals for each picture to produce a count signal. A second comparator compares the count signal with a second threshold value to produce a change detection signal representative of the drastic change when the count signal is greater than the second threshold value.
The conventional method is, however, defective in that the change detection signal is produced even when a large object body moves so that the large object body has different positions in a current picture and in a previous picture which are two adjacent ones of the successive pictures. The conventional method is therefore incapable of accurately detecting a drastic change.